The transfer of ultra-high frequency power presents many problems, the most important one being the prevention of radiation from the conductors leading from a source of power to a measuring system or a transmission device such as an antenna or a heating system. In this regard, the concentric line has been found to be quite suitable provided the impedance of the line is constant and does not vary from a desired input-output value. Any variation in impedance results in reverse flow reflections which reduce the efficiency, increase radiation, and introduce errors into any measuring systems or transmission device that may be employed.
Bends in a concentric line should have the same insulator-dielectric as the linear portions of the system, but these bends are very expensive to fabricate and difficult to hold to the proper dimensions. Dielectric powder material has been used in the bends but such a construction has its problems and unless the powder is firmly packed, reflections will occur.
Current sophisticated microwave systems have created the need for high-performance broadband interconnecting devices. This requirement has been substantially met by several series of straight connectors. However, angular connectors have not been utilized due to their inferior voltage standing wave rates (VSWR) characteristics over a limited frequency range. Present and future systems, with increased emphasis being placed on packaging factors, will demand the use of right angle connectors whose electrical performance is comparable to similar types of straight connectors.
The usual procedure in forming connectors of this type has been to use a two-piece contact and insulator design to form the right angle, and solder the two straight contacts together. The cavity surrounding the joint is then filed with insulating material, or the cavity may be left unfilled, with air acting as the dielectric. This device gives poor electrical performance due primarily to the varying relationships between the outer diameter of the inner conductor and the inner diameter of the outer conductor.
Other means of forming right angles has been with the use of a singular contact in conjunction with an insulator, or with the dielectric of the cable itself forming the bend. In the latter case, a metallic insert encompassing the apex of the bend is utilized as the outer conductor. The insert is shaped so that it provides an equidistant surface with respect to the inner conductor around the bend, however, outer conductor irregularites at the inside portion of the bend result in impedance discontinuities. In addition, this configuration is limited by the size of the cable dielectric core, due to the difficulty encountered in bending cables of approximately 0.2 inch (5.1 mm.) or more in diameter.
Another design of a right angle connector is described in U.S. Pat. No. 3,528,052, which issued to A. R. Brishka on Sept. 8, 1970 and is assigned to the same assignee of the subject invention. This design consisted of a singular contact surrounded by a TFE dielectric forming a 90.degree. bend terminating in 2 mating faces. The outer diameter of the dielectric was 0.306 inches (7.77 mm.) bent around a radius of 0.125 inch (3.17 mm.). A metallic insert was machined to surround the apex of the bend and all remaining cavities were filled with fine metallic particles. Test results indicated the addition of the metallic particles improved the performance of the connector considerably. Consequently, the insert was completely replaced by metallic particles. The connector exhibited even better electrical characteristics, however, it was mechanically unfeasible to distribute the particles efficiently in order to completely surround the dielectric. The use of epoxies was limited by the unavailability of those which would exhibits high electrical conductivity. These problems were solved by plating the dielectric with silver thus providing a continuous outer conductive coating. Mechanical and electrical tests indicated that a low impedance section existed in the region of the bend. The optimum configuration for the elbow at the completion of the bending process would be a condition such that the center conductor be equi-distant from the outer surface of the dielectric at all planes which are perpendicular to the axis of the bent assembly. However, due to the sharpness of the bend and the physical properties of the materials used, the above condition does not exist. Instead, when the assembly was bent, the dielectric stretched and the center conductor tended to move radially outward at the apex of the bend. This resulted in a lower cross-sectional area at the elbow and thus, when the assembly was plated or surrounded by conductive particles, the impedance at this section was lowered. In order to achieve a satisfactory electrical performance, compensation in this region was required for the impedance discontinuity. To accomplish this, a method (simulating an increased outer conductor) of introducing a high impedance section for compensation purposes was effected by removing the conductive material at the apex of the elbow. Improved VSWR and impedance characteristics were obtained, however, the range of frequency was limited to a usable frequency range of up to 10 GHz. In addition to the limitation of the frequency range of the last mentioned prior art design, it is noted that such design is relatively complicated to construct in that the amount of conductive material removed is very critical. Thus the cost of manufacture is relatively high and maximum quality control must be exercised during the manufacture of the design. Furthermore, the limited frequency range of this prior design limits its capability of use for certain high radio frequency applications greater than 10 GHz, for example in the range 12 --18 GHz.
More particularly, the subject invention relates to a 90.degree. radio frequency coaxial connector having improved radio frequency performance that is achieved by using an air filled dielectric, a smooth radio transition of the outer conductor at the 90.degree. bend, and a preformed smooth radio transition at the center conductor. A matched characteristic impedance section throughout the 90.degree. transition is achieved by maintaining constant diameter ratios between the inner and outer conductors. The inner conductor is preformed before assembly thus maintaining the heat treated spring properties required for connector interfaces requiring spring member female inner conductors. The subject design also employs non-heat treated inner conductors for interfaces requiring male pin inner conductors. The use of heat treated elements facilitates the manufacture and accordingly reduces the cost of manufacture of the subject connector.
In order to maintain constant inner and outer diameter ratios, thus maintaining a matched characteristic impedance, the outer diameter of the inner conductor is held concentric with the inner diameter of the outer conductor by means of dielectric supports disposed in recesses at the ends of the outer conductor. The use of an air dielectric allows for a constant dielectric constant to maintain the matched characteristic impedance which may otherwise be distorted when employing solid material dielectrics. The inner face of the subject connector may be of varying configurations and the back end thereof may accept a cable or a panel, according to the specific application.